Succession in the Brazilian Amazon depends on prior land-use history. Abandoned clearcuts become dominated by Cecropia trees and exhibit species replacements characteristic of natural succession in ...forest lightgaps. In contrast, abandoned pastures are dominated by Vismia trees that inhibit natural succession for a decade or more. Here we explore how advance regeneration and limited seed dispersal may contribute to the arrested succession in Vismia-dominated stands. Vegetation surveys showed that every Vismia stem in 3–8 year old Vismia stands originated as a re-sprout. In Cecropia stands, all tree species, including Vismia, originated mostly from seeds, after deforestation and abandonment. The 100% re-sprouts of Vismia in the abandoned pastures confirms that Vismia dominance results from re-sprouting following pasture fires. Seed rain in both Vismia and Cecropia dominated stands was limited almost exclusively to second growth species already reproducing in those stands, suggesting that the bats and birds foraging there were not bringing mature forest seeds into the second growth, but simply feeding and depositing local second growth species. As dispersal was similar in both stand types, dispersal differences cannot account for the ongoing dominance of Vismia relative to the ongoing successional transitions in Cecropia stands. Overall, advance regeneration in the form of Vismia re-sprouts is much more likely to be the driver of Vismia dominated succession than differential dispersal of mature forest seeds. In order to avoid extensive forest conversion into unproductive Vismia wastelands in the Amazon Basin, forestry permits for harvesting timber should include restrictions on subsequent anthropogenic degradation, such as conversion to pasture and prescribed burning.
Logistic multiple regression models were constructed for turkey oak crown survival and resprouting in two experimental fires. Crown survival patterns were similar in the mild and the more intense ...fire. Crown survival was positively related to @'turkey oak diameter at breast height (dbh),@' and @'distance to the nearest large longleaf pine@'; it was inversely related to the @'dbh of the nearest pine.@' The crowns of small turkey oaks (2.5-5.5 cm dbh) rarely survived the intense fires fueled by needle litter in the vicinity of longleaf pines, while large turkey ocaks (>10 cm dbh) had high crown survival regardless of location. In the mild fire, pines affected the survival of small turkey oaks within a distance of at least 10 m, while in the hotter fire pines appeared to affect the survival of small turkey oaks within at least 25 m. In the mild fire, 68% of the crown-killed oaks resprouted, and the probability of resprouting was inversely related to both @'turkey oak dbh,@' and @'distance to the nearest pine.@' Most trees that failed to resprout had delayed crown mortality. In the hotter fire, 95% of crown-killed oaks resprouted, and resprouting was inversely related to @'turkey oak dbh.@' Although the pyrogenicity of longleaf pine also leads to segregation of adult pines and their seedlings, most oaks are adversely affected by fires within the zone of maximum pine seedling recruitment. Thus, reduced competition from oaks may increase the fitness of longleaf pines and favor selection for pyrogenicity.
This study characterizes the flowering and fruiting phenology of the 13 most common pioneer tree species in early successional forests of the Central Amazon. For each species, 30 individuals, 10 each ...in three secondary forests, were monitored monthly for four years at the Biological Dynamics of Forest Fragments Project, north of Manaus. Five species showed nearly continuous flowering and fruiting throughout the study, indicating that resources were available to pollinators and dispersers on a regular basis. The other eight species showed stronger seasonality in reproduction, seven of them annually, and one supra-annually. Overall, flowering was concentrated in the transition from the dry to the rainy season and fruiting was concentrated in the rainy season. There was no relationship between reproductive phenology and tree pollinator type or dispersal mode. Reproductive phenology was remarkably consistent year to year. The pioneer community showed a variety of phenological patterns but as a whole tended to be characterized by annual flowering and fruiting, either continuously or seasonally, thereby fitting generalizations of pioneer species relative to mature forest species.
Background: The tradeoff between seed mass and seed number per plant is widely established for different taxa, guilds, and communities. Relative to primary forest species, pioneer species generally ...produce large numbers of small seeds. Aims: We tested if the relationship between seed mass and seed number was connected to the fruit variables – namely, fruit mass and fruit number per tree – in order to evaluate tradeoffs in seed packaging. Methods: Seed mass and seed number per tree as well as fruit mass and fruit number per tree were measured for 12 pioneer species common to secondary forests in the central Amazon. Results: Seed mass, seed number, fruit mass, and fruit number varied by several orders of magnitude among species. Seed number was explained only partially by seed mass alone (R ² = 0.55), but nearly completely by the combination of seed mass, fruit mass and fruit number (R ² = 0.94). The number of seeds per fruit was positively correlated with fruit mass and total seed number per tree and negatively with seed mass and fruit number. Seedling and adult abundances were most dependent on fruit number and fruit mass, not seed number and seed mass. Conclusions: Biomass tradeoffs between seed mass and seed number are partially dependent on seed packaging, specifically seeds per fruit, fruit mass and fruit number per tree for pioneer trees in the central Amazon.
The archaeology of Bruce Trigger Williamson, R. F; Bisson, Michael S
The archaeology of Bruce Trigger,
c2006, 20060824, 2006, 2006-08-24
eBook
In The Archaeology of Bruce Trigger, leading scholars discuss their own approaches to the interpretation of archaeological data in relation to Trigger's fundamental intellectual contributions
A composição florística de uma floresta secundária dominada por Vismia na Amazônia central foi estudada e comparada de acordo com sua composição ao banco de sementes no solo. A área apresentou um ...total de 20 espécies arbóreas, sendo Vismia o gênero dominante em indíce de valor de importância, densidade relativa e área basal. O banco de sementes coletado na área apresentou germinação de apenas 17 espécies, todas pioneiras, entre as quais metade foi de herbáceas e a outra metade de lenhosas. A composição do banco de sementes foi em geral característica de estágios sucessionais, com forte influência do histórico de pastagem, presença de espécies pioneiras e um elevado número de herbáceas e gramíneas. Os gêneros Goupia e Laetia estiveram ausentes no banco mesmo com indivíduos adultos representados no dossel. Os três gêneros com maior representação no banco de sementes em relação ao dossel foram Cecropia, Bellucia e Trema, os quais provavelmente germinaram de sementes chegadas depois do desenvolvimento do dossel de Vismia. As parcelas que tiveram o dossel removido refletiram muito bem a composição da vegetação estabelecida na área, onde sementes de espécies da floresta mais madura não germinaram. Desta forma, o retorno à floresta primária deverá ser um processo lento e dependente de fontes de sementes próximas, além da presença de dispersores capazes de contribuir com a chuva de sementes.
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